Yes, I have a 1D and yes it's 1/500 officially. But it has an electronic shutter which goes to 1/16000 seconds and theoretically you can sync to that if you want... In practice, flash duration and the flash color shift during release limit it to about 1/2000 in my tests. Faster than that and you get reduced flash output & color casts because the flash has gone off only partially before the CCD stops collecting light.
Of course if you use a TTL flash, the camera and flash will conspire to limit you to the spec'd 1/500s. Which is still great. The 4 Mpx is not too hot though...